If you tell us the ways you've already listed about how sociologists calculate prejudice, we may be able to help you find OTHER ways.

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Harvard's IAT exams, test your prejudice by presenting images of light or dark skinned people and associations with GOOD or BAD words.
Also, sociologists have used video games that require a subject to press one button to shoot a dangerous or another to classify an image as harmless. The images were both white and black people carrying various objects, such as cell phones, wallets, guns, etc..